The present invention relates generally to plating and etching, and, more specifically, to electrodeposition of a film of uniform thickness and composition.
Electroplating is a common process for depositing a thin film of metal or alloy on a workpiece article such as various electronic components for example. In electroplating, the article is placed in a suitable electrolyte bath containing ions of a metal to be deposited. The article forms a cathode which is connected to the negative terminal of a power supply, and a suitable anode is connected to the positive terminal of the power supply. Electrical current flows between the anode and cathode through the electrolyte, and metal is deposited on the article by an electrochemical reaction.
In many electronic components it is desirable to deposit the metal film with a uniform thickness across the article and with uniformity of composition. However, the electroplating process is relatively complex and various naturally occurring forces may degrade the electroplating process. Most significantly, the electrical current or flux path between the anode and the cathode should be relatively uniform without undesirable spreading or curving to ensure uniform electrodeposition. Furthermore, as metal ions are depleted from the electrolyte, the uniformity of the electrolyte is decreased and must be suitably corrected to avoid degradation of the electroplating process. And, debris particles are generated in the chemical reactions which can degrade the metal film on the article upon settling thereon.
Conventional electroplating equipment includes various configurations for addressing these as well as other problems for ensuring relatively uniform electroplating. Suitable circulation of the electrolyte is required for promoting electroplating uniformity, and care is required for properly aligning the cathode and anode to reduce undesirable flux spreading. For example, one type of conventional electroplating apparatus mounts the cathode at the bottom of an electrolyte bathing cell, with the anode being spaced above and parallel to the cathode. Since the article is at a common depth in the cell, the electroplating process is less susceptible to vertically occurring variations in the process due to buoyancy or gravity effects or other convection effects occurring during the process. For example, ion depletion in the electrolyte adjacent to the article will create local currents which will have a common effect along the horizontal extent of the article, but can vary vertically.
And, in the electrodeposition of magnetic materials, e.g. permalloy, resulting gases are produced in the process which result in bubbles being generated at the article surface. Of course, bubbles are buoyancy driven upwardly, and horizontally positioning the article reduces adverse effects therefrom.
Enhanced uniformity in metal deposition is also typically promoted by suitable agitation of the electrolyte in the cell. However, agitation by a unidirectional flow of the electrolyte is typically undesirable since it can cause monotonically decreasing mass-transfer effectiveness along the direction of flow.
Although horizontally positioned cathodic articles typically result in relatively uniform electrodeposition, the articles are more prone to the settling thereon of debris particles which degrade the article. And, the various conventional configurations for horizontally electroplating an article have varying degrees of complexity which increases the difficulty in mass producing electrodeposition articles. It is desirable to provide not only high uniform thickness and composition in an electrodeposition article, but also do so in an apparatus capable of high-volume manufacturing, and preferably using automated handling equipment.